This invention relates to thermoplastic molding composition and particularly to compositions containing a compatibilized blend of an aromatic polycarbonate resin and a graft copolymer. The composition is useful in making molded articles having improved energy absorption at low temperatures.
Thermoplastic molding compositions containing polycarbonates (PC) and ABS polymers have been known for some time. Such compositions which find use in a variety of applications are available commercially, for instance, from Bayer Corporation under the Bayblend trademark. Also, the art is noted to include a large number of relevant patents, including U.S. Pat. No. 5,420,181 which disclosed stabilized PC/ABS system, and U.S. Pat. Nos. 5,672,645 and 5,674,924 which disclosed flame resistant PC/ABS molding compositions. However, the energy absorption at low temperatures characterizing these compositions is recognized to be inadequate for some applications. While it is possible to increase the energy absorbing characteristics of the composition by adding rubber, this often results in decreased modulus. It has now been found that the incorporation of a particular compatibilizer in the polycarbonate/ABS blend improves its energy absorption characteristics without the addition of more rubber. U.S. Pat. No. 4,713,415 which disclosed a compatibilizing agent for a polymeric system containing nylon and ABS is relevant in the present context.
The present invention concerns a thermoplastic molding composition comprising:
A) 20 to 90 parts by weight (pbw) of an aromatic polycarbonate resin,
B) 4.5 to 70 pbw of a vinyl copolymer,
C) 5 to 70 pbw of a graft polymer, and
D) 0.5 to 5 pbw of a compatibilizer.
Articles molded from the inventive composition are characterized in their improved capacity to absorb energy at low temperature.